(() => {
    // 抽象类
    class Animal {
        // 实例化对象
        run() {
            console.log('run ....');
        }
    }
    // 定义一个子类(派生类)
    class Dog extends Animal {
        eat() {
            console.log('dog eat 骨头');
        }
    }
    const dog = new Dog();
    dog.eat();
})();
